1. Field of the Invention
The invention relates to the field of semiconductor fabrication processes and more particularly to a method and apparatus for monitoring the angular rotation rate of a spin rinse dryer by placing an identifying mark on a designated wafer carrier and monitoring the identifying mark with an external monitoring apparatus such as a tachometer.
2. Description of the Relevant Art
Semiconductor integrated circuits have been widely employed in virtually every type of electronic device since the early 70's. In the typical semiconductor fabrication process used to fabricate these integrated circuits, a single crystal semiconductor wafer, typically comprised of silicon, is fabricated into integrated circuits by forming a large number of individual circuit elements such as resistors, capacitors, and transistors, and, thereafter, selectively interconnecting the individual circuit elements with one or, more typically, multiple levels of interconnect layers. Even the most routine fabrication process requires a great many process steps that must be carried out with exacting precision in the cleanest of environments if the final product is to be functional. The various parameters associated with each step of the fabrication process must be closely monitored by the fabrication facility personnel to prevent undesirable deviations from specified optimum levels of the parameters.
To provide the accurate monitoring of various deposition, etch, and photolithography steps, semiconductor equipment manufacturers typically incorporate highly sophisticated monitoring equipment on each machine that is installed in a customer's fabrication facility. The monitoring equipment provides the feedback necessary for the manufacturer to insure an adequate yield from the process (where yield refers to the percentage of devices on a wafer that are functional). While many process steps require semiconductor fabrication equipment, such as deposition machines, photo aligners, and implant machines, costing hundreds of thousands of dollars, perhaps an equal number of process steps, or process sub-steps, involve equipment of far less complexity and cost. An example of a piece of equipment that fits this description is the well known spin rinse dryer found in multiple locations within virtually every fabrication facility.
Conventional spin rinse dryers are used extensively in conjunction with wet processing steps to rinse the wafers with ultra pure deionized water and to subsequently spin dry the wafers. Despite their relative simplicity in comparison to implanters, CVD reactors, photo aligners, plasma etchers, and various other pieces of process equipment, spin rinse dryers are an important component of any fabrication process and maintaining the highest feasible control over the parameters associated with spin rinse dryers is critical. The three most significant process parameters in any spin rinse dry operation are the duration of the process, the resistivity, and the angular rotation rate of the dryer chamber (most commonly reported in terms of revolutions-per-minute or "RPM").
To insure the highest quality, these parameters should be regularly calibrated to detect and minimize any drift in the reported vs. actual value of the parameters. Therefore, it would be highly desirable to implement an economical and practical method for monitoring, adjusting, and calibrating the duration, resistivity, and angular rotation rate of each spin rinse dryer in a fabrication facility. While techniques and processes for monitoring the resistivity and duration are widely available, the monitoring of the angular rotation parameter has been largely ignored resulting in less control over the spin rinse dry process.